set linker options only on PPC, not needed on x86

browser/app/moz.build

@@ -71,7 +71,9 @@ if CONFIG['MOZ_LINKER']:
 if CONFIG['HAVE_CLOCK_MONOTONIC']:
     OS_LIBS += CONFIG['REALTIME_LIBS']
 
-OS_LIBS += ['-Wl,-stack_size,0x40000000,-stack_addr,0xf0000000']
+# we build only on Darwin anyway
+if CONFIG['OS_ARCH'] == 'Darwin' and CONFIG['CPU_TYPE'] == 'ppc':
+    OS_LIBS += ['-Wl,-stack_size,0x40000000,-stack_addr,0xf0000000']
 
 if CONFIG['GNU_CXX']:
     CXXFLAGS += ['-Wshadow']